you don't pay for volts you pay for watt-hours, voltage is meaningless without knowing how much current is drawn. If you have stray voltage, which btw is not uncommon, you are not using a significant amount of power in that sense though so I would write that off as "negligible" power usage. I've have solar though so I'm not sure what the tiered rates are as they just tell me a net usage and cost each month then bill me at the end of the year (this year I'm at around $500 for electricity which isn't half bad!).
To answer your questions, yes PG&E is seasonal. Depending upon where you live you get more of an allowance in the summer than the winter, unless you live on the coast/peninsula then it's pretty dead even since we don't "need" AC and we're expected to have natural gas hookups.
Another possibility for high cost is to think where the tank is located, if you're one of those people who don't mind the house getting colder, or you have a sump in a garage/basement then the cold weather absolutely will affect you as your heaters will work that much harder. I notice that on my solar usage, I go from $100/month when it's cold/cloudy/not making much power to $3 when it's warm/sunny and heaters don't need to work too hard.